Angled flying lead wire bonding process

ABSTRACT

A method is described having the steps of providing a surface having a plurality of wire bondable locations, wire bonding a wire to each of the wire bondable locations using a wire capillary tool; controlling the position of the capillary tool with respect to the substrate; after forming a wire bond of the wire to the wire bondable location moving the capillary tool relative to the surface as the capillary tool is moved away from the surface to form a wire having a predetermined shape.

FIELD OF THE INVENTION

[0001] The present invention is directed to a process for bonding wiresto surfaces, for example, to form electronic device probes, or to formelectrical connections on electronic circuit devices and particularly towires that are bonded at one end with the other end free.

BACKGROUND OF THE INVENTION

[0002] Wire bonding techniques were first developed back in the 1950'sfor connecting germanium transistors to other electronic devices. Wirebonding techniques continue to be used for the vast majority ofintegrated circuit device connections. Thermal energy, mechanical forceand ultrasonic vibrations are used to bond the tiny wires to the deviceterminals.

[0003] The Angled Flying Lead (AFL) wire bonding process disclosedherein uses the same basic processes that are used for a standardthermosonic ball bonding operation and it was developed for fabricatinga variety of area array and peripheral interconnections including highdensity land grid array connectors and high density IC probes.

[0004] In conventional wire bonding, schematically shown in FIG. 1, afree end of a wire is ball bonded to a contact pad on a surface. Thewire is bent over and wedge bonded to another pad. The wire joining thetwo pads is curved. The shape of the curve is determined by the distancebetween the two pads which are joined. If the wire joining the two padsare severed, two wires having different shapes are formed. If it isdesired that the wires bonded to the surface be used as an electronicdevice probe (as described herein) or to interconnect an array ofcontact pads on a first surface to another array of contact pads on asecond surface which is facing the first surface, the conventional wirebonding process is not useful to fabricate such structures. To fabricatea probe for an electronic device using wires (probe wires) bonded to asurface, one end of the wire is bonded to contact pads on a supportsubstrate for the probe wires. The other ends of the probe wires must bepositioned so as to be able to contact the contact pads on device beingtested. When an electronic device probe is moved into engagement withthe contact pads of the device under test, the probe wires preferablyflex so that the free end (probe tip) of the wires wipe across thesurface of the contact pad being probed. The wiping action permits theprobe tip to make good electrical contact to a contact pad. Since aprobe is used many times, the probe tips of the probe wires make manythousands (preferably greater than 1000, more preferably greater than10,000, most preferably greater than 100,000) engagements anddisengagements with contact pads on devices under test resulting in manyrepeated bendings. The probe tip also must be flexible enough to achievethe desired degree of wiping, withstand many engagements withoutdeforming and be sufficiently compressible to without deformation.Applicants invention provides a method and approach which can reliableform many probe wires to a desired predetermined shape to satisfy allthese requirements.

[0005] There is a need for a technique to form wires bonded to surfaceswhere the wires can be formed to have any desired shape to providecertain desired properties. The wires can be bonded to electricalcontact pads on a surface drawn away from the surface and cut to have afree end. The wires are bent so that the free ends are placed in apredetermined shape which provide advantageous properties, such as adesired flexibility.

SUMMARY OF THE INVENTION

[0006] It is the object of the present invention to provide a processfor bonding wires to an electronic circuit device with one end of thewire attached to the surface of the device and the other end of the wireextending away from the surface of the device.

[0007] Another object of the present invention is to provide a processfor bonding wires to an electronic circuit device with the wires formedat an angle to the surface of the device.

[0008] A further object of the present invention is to provide a processfor bonding wires to an electronic circuit device with the wires havingcurved features.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] These and other objects, features, and advantages of the presentinvention will become apparent upon further consideration of thefollowing detailed description of the invention when read in conjunctionwith the drawing figures, in which:

[0010]FIG. 1 shows the standard wire bonding process steps.

[0011] FIGS. 2-6 show the preferred embodiment of the angled flying leadwire bonding process.

[0012] FIGS. 7-8 show the alternate embodiments of the angle flying leadwire bonding process.

[0013] FIGS. 9-12 show various configurations of flying lead wiregeometries.

[0014]FIG. 13 shows a variety of shapes of the wire tip ends created tofacilitate the engagement of wire tips with electronic device pads.

[0015]FIG. 14 schematically shows a frame structure to be used tocontrol the wire position accuracy and, in the mean time, providematched thermal coefficient to that of silicon at elevated wafer testingtemperatures.

[0016]FIG. 15 is a schematic diagram showing the structures according tothe present invention in testing apparatus.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The standard wire bonding operation is shown in FIG. 1 and startsby forming a ball on the end of a (preferably) gold wire 110 that isthreaded through a hollow pointed ceramic tool called a capillary 115.The ball 112 is pressed against the first bonding surface 116 ofsubstrate 118 while the substrate 118 is heated from below andultrasonic energy is applied through the capillary 115 as shown in step1 of FIG. 1. The metallurgy on the surface of the substrate is criticalto the wire bonding process. After ball bonding the wire to the firstsubstrate surface 116, the capillary 115 is raised while the substrateis moved (shown by arrow 120) to create a loop shape in the wire (FIG.1—step 2). The capillary 115 is then lowered to press the side 124 ofthe wire against the second substrate 126 surface 128 to form the secondbond or wedge bond 130 (FIG. 1—step 3). The capillary is raised slightlyindicated by arrow 132 and a mechanical clamp is actuated to hold thewire in place while the capillary is raised again to break the wire atthe end of the wedge bond 134 (FIG. 1—step 4). The ball is formed on theend of the gold bond wire by placing an electrode below the tip 136 ofthe wire and using a high voltage electrical discharge to melt the endof the wire (FIG. 1—step 5).

[0018]FIG. 2 shows a cross section of an electronic circuit component(11) and several angled flying leads (10) attached to the first surface(12) of the component (11) according to the present invention. Theangled flying leads (10) can be attached to a variety of differentelectronic circuit components (11). The angled flying leads (10) arebonded to metallized circuit pads (13) on the first surface (12) of theelectronic circuit component (11). The electronic circuit component (11)must provide a rigid base for the thermosonic wire bonding process to besuccessful. FIGS. 1, 2, and 3 of the angled flying lead wire bondingprocess are essentially the same as a standard thermosonic wire bondingprocess. An electrical discharge (22) from an electronic flame off (EFO)unit (21) is used to melt the end of the bond wire (16) extendingthrough the tip of a ceramic capillary tool (15). The electricaldischarge (22) is controlled to provide a consistent sized ball (14) onthe end of the bond wire (16).

[0019]FIG. 3 shows the ceramic capillary tool (15) used to press theball shaped end of the bond wire (16) against the metallized pad (13) onthe surface of the electronic circuit component (11). Ultrasonic energy(30) applied through the ceramic capillary tool (15) and thermal energyapplied through the base holding the electronic circuit component (11)in used to form a ball bond (19) between the bond wire (16) and themetallized pad (13) on the surface of the electronic circuit component(11).

[0020]FIG. 4 shows the movement of the electronic circuit component (40)and the movement of the ceramic capillary tool (41). The movement of theelectronic circuit component (40) is used to define the offset betweenthe free end (18) of the angled flying lead (10) and the ball bond (19)attached to the electronic circuit component (11). The movement of theceramic capillary tool (15) provides sufficient slack in the bond wireto minimize stress to the ball bond (19) during the subsequentoperations.

[0021]FIG. 5 shows additional movement of the ceramic capillary tool(50) that is used to form the angled and curved geometry (17) of theangled flying lead (10). The movement of the capillary tool (50) must becontrolled to prevent deformation of the adjacent angled flying leads(10).

[0022]FIG. 6 shows the shear blade (60) that is used to sever the bondwire (62) to form the free end (18) of the angled flying lead (10). Theshear blade (60) is precisely located (61) to ensure accuratepositioning of the free end (18) of the angled flying lead (10). A clampis used to hold the bond wire while the ceramic capillary tool (15) israised (62) and the bond wire is severed at the tip of the shear blade(60).

[0023]FIG. 7 shows the retraction of the shear blade (70) and the upwardmovement of the ceramic capillary tool (71). The end of the bond wire(72) extending through the tip of the ceramic capillary tool is used forthe next ball bond and the process is repeated to form the desirednumber of angled flying leads (10) on the electronic circuit component(11).

[0024]FIG. 8 shows an alternate embodiment of the wire cutting processshown in FIG. 5. The alternate wire cutting process shown in FIG. 7 usestwo shear blades (80, 83) instead of a single blade. The movement andpositioning (81, 84) of the two blades (80, 83) is synchronized to nickthe wire on opposites sides and allow the wire to fracture at thispoint. The double-blade configuration can be used for cutting wires thathave a high tensile strength. The two blade configuration alsosignificantly improves wire positioning accuracy.

[0025]FIG. 9 shows a second alternate embodiment of the wire cuttingprocess similar to the two blade process shown in FIG. 8. The secondalternate wire cutting process shown in FIG. 9 is used for creatingstraight wires (100) attached to an electronic circuit component (11).The movement and positioning (91, 94) of the two blades (90, 93) iscontrolled to nick the opposite sides of the wire and allow the wire tofracture at this point.

[0026]FIG. 10 shows three wire configurations (120, 121, 122) attachedto an electronic circuit component (11) using the angled flying leadwire bonding process. All three of the wires (120, 121, 122) are createdwith the height (124) from the surface of the electronic circuitcomponent (11). The three wire configurations include a straight wire(120), an angled wire (121), and a wire (122) with a section parallel tothe surface of the electronic circuit component (11). Variations ofthese three wire configurations (120, 121, 122) can be created includingwires with different angles (123) and different wire offset (125)dimensions as shown on the angled wire (121).

[0027]FIG. 11 shows four wire configurations (130, 131, 133, 134)attached to an electronic circuit component (11) using the angled flyinglead wire bonding process. The four wire configurations include twostraight wires (130, 131) with different wire heights (132, 136) and twoangled wires (133, 134) with two different wire heights (135, 137).

[0028]FIGS. 12 and 13 schematically show a variety of wire shapes (141,142, 143, 144, 145, 146, 147, 148) practiced by the present invention.The different wire shapes are created by controlling both thedown-movement of the capillary tip and the off-set move of the wirebonding stage. The shapes continuously curved, piece wire curved, piecewire linear and combinations thereof.

[0029]FIG. 13 schematically shows several shapes and geometries of thewire tip ends, such as straight (167), straight with pointed contact(166), straight with point contact deposited with a suitable contactmetallurgy (165), straight end with sharp spikes (164) and depositedwith a suitable contact metal (163), ball-shaped (162), ball-shapeddeposited with a suitable contact metallurgy (161) and deposited withsharp spikes (160) at the contact ends.

[0030]FIG. 14 schematically shows a frame structure (150, 153) which canbe tailored to match the thermal expansion coefficient of silicon andother materials. The wire tip ends (152) need to be maintained inprecise position before and after engagement with electronic device padsat up to 180° C. The various contact geometries as shown in the figureare fabricated at the end of wires to facilitate various contact andtest applications.

[0031]FIG. 15 is a schematic diagram showing the structures according tothe present invention in testing apparatus. The testing apparatus 208has a measn 207 for disposing the probe tip ends 210 in contact withcontact locations 212 on the device under test 204 which is disposed onsupport 206.

[0032] The minimum spacing between angled flying leads is dependent onthe diameter of the bond wire that is used and the size and geometry ofthe capillary tip used for bonding the wires. Smaller diameter wires canbe bonded closer together. The capillary tip geometry can be modifiedusing a bottleneck configuration or a side relief to allow closerbonding of the flying leads. The maximum height for an angled flyinglead is also determined by the diameter and material properties of thebond wire and the offset distance between the ball bond and the free endof the wire. Small diameter wires (0.001 to 0.002 inch) are bettersuited to shorter leads and larger diameter wires (0.002 to 0.003 inch)are better suited to longer leads. The key material properties of thewire include the stiffness and the tensile strength. The wire propertiescan be controlled by the alloys used in the wire material and theelongation factor used for forming the wire. The structures fabricatedaccording to the methods of the present invention

[0033] The teachings of copending U.S. application Ser. No. 09/088,394filed Jun. 1, 1998 and U.S. Pat. No. 5,371,654 are incorporated hereinby reference.

[0034] While we have described our preferred embodiments of ourinvention, it will be understood that those skilled in the art, both nowand in the future, may make various improvements and enhancements whichfall within the scope of the claims which follow. These claims should beconstrued to maintain the proper protection for the invention firstdisclosed.

What is claimed is:
 1. A process for making angled flying lead wirestructures attached to an electronic circuit component comprising: afirst process step used to bond said flying lead wire to a first surfaceof said electronic circuit component; a second process step where themovement of the wire capillary tool and the XY stage are controlled toform a desired shape in said flying lead wire; a third process stepwhere a single shear blade mechanism is positioned in contact with saidflying lead wire; a forth process step where said capillary tool israised to tension said wire against said shear blade and sever saidwire.
 2. A process according to claim 1, further including forming saidflying lead wires with a plurality of angles relative to the surface ofsaid electronic circuit component.
 3. A process according to claim 2,further including forming said flying lead wires with a plurality ofheights relative to the surface of said electronic circuit component. 4.A process according to claim 3, further including forming said flyinglead wires to have a shape selected from the group consisting of linear,piece wise linear, continuously curved, and combinations thereof.
 5. Aprocess for making flying lead wire structures attached to an electroniccircuit component comprising bonding said flying lead wire to a firstsurface of said electronic circuit component; controlling the movementof the wire capillary tool and the XY stage to form a desired shape insaid flying lead wire; shearing said flying lead wire with a doubleshear blade mechanism positioned on opposite sides of said flying leadwire and creating a small nick on opposite side of said wire; saidcapillary tool is raised to sever said wire at the point where saidnicks were formed by said shear blades, said flying lead wires havingwire tip end.
 6. A process according to claim 5, further includingforming said flying lead wires with a plurality of angles relative tothe surface of said electronic circuit component.
 7. A process accordingto claim 6, further including forming said flying lead wires with aplurality of heights relative to the surface of said electronic circuitcomponent.
 8. A structure according to claim 1 or 5, further includingmaintaining said flying lead wire in a predetermined position bydisposing a sheet of material having a plurality of openings thereinthrough which said flying lead wires project.
 9. A structure accordingto claim 8, wherein a compliant frame structure is used to support saidsheet of materials.
 10. A structure according to claim 8 wherein saidsheet is spaced apart from said surface by an electronic component toprovide flexible support.
 11. A structure according to claim 8 whereinsaid sheet is spaced apart from said surface of the electronic componentby a rigid support, said rigid support serves as a stand-off, or hardstop, to limit the degree of movement of said wire tip end in adirection perpendicular to said surface.
 12. A structure according toclaim 8 wherein said sheet is spaced apart from said surface of theelectronic component by a support with the composite structure of both arigid and a compliant layer.
 13. A structure according to claim 10wherein a space between said surface of the electronic component andsaid sheet is filled with a compliant medium.
 14. A structure accordingto claim 13 wherein said the compliant medium is an elastomericmaterial.
 15. A structure according to claim 13 wherein said thecompliant medium is a foamed polymer material.
 16. A structure accordingto claim 10 wherein said flexible support is selected from the groupconsisting of a spring and an elastomeric material.
 17. A structureaccording to claim 8 wherein said wire tip ends comprise a structureselected from the group consisting of a protuberance, a sphericalcontact geometry, a straight contact end, a sharp spike, multiple sharpspike, sharp nodules and the combination of the above.
 18. A structureaccording to claim 8 wherein said wire end tips are coated with amaterial selected from the group consisting of Ir, Pd, Pt, Ni, Au, Rh,Ru, Re, Co, Cu, and their alloys.
 19. A structure according to claim 8wherein said angle flying lead wire is coated with a material selectedfrom the group consisting of Ir, Pd, Pt, Ni, Au, Rh, Ru, Re, Co, Cu, andtheir alloys.
 20. A structure according to claim 8 wherein said sheetcomprises materials selected from the group consisting of Invarlaminate, a Cu/Invar/Cu laminate, molybdenum laminate.
 21. A structureaccording to claim 8 wherein said sheet comprises a material selectedfrom the group consisting of a metal, a polymer, a semiconductor anddielectric.
 22. A structure according to claim 20 wherein said the sheetis overcoated with a polymer layer.
 23. A structure according to claim20 wherein the sheet is overcoated with an insulating layer.
 24. Astructure according to claim 20 wherein the sheet is overcoated with athin compliant polymer layer.
 25. A structure according to claim 20wherein the sheet is laminated between two insulating layers.
 26. Anapparatus for using said structure of claim 8 to test an electronicdevice comprising: means for holding said structure of claim 1, meansfor retractably moving said structure of claim 1 towards and away fromsaid electronic device so that said wire tip ends contact electricalcontact locations on said electronic device, and means for applyingelectrical signals to said elongated electrical conductors.
 27. Aprocess according to claim 1 wherein said electronic circuit componentis a substrate having an electrical conductor pattern.
 28. A methodcomprising: providing a substrate surface having a plurality of wirebondable locations; wire bonding a wire to each of said wire bondablelocations using a wire capillary tool; controlling the position of saidcapillary tool with respect to said substrate; after forming a wire bondof said wire to said wire bondable location moving said capilary toolrelative to said surface as said capillary tool is moved away from saidsurface to form a wire having a predetermined shape.